1. Field of the Invention
The present invention relates to a process for producing diglycerides which comprises partially hydrolyzing fats and oils and adding glycerol to the decomposition product to conduct esterification.
2. Discussion of the Background
Diglycerides are used as additives for improving the plasticity of fats or as bases in the fields of foods, medicines, cosmetic preparations, and the like.
Examples of processes for producing diglycerides include the esterification or transesterification method and the glycerolysis method.
A representative example of the esterification or transesterification method is disclosed in JP-B 6-65311, in which fatty acids or lower alcohol esters thereof are reacted with glycerol in the presence of an immobilized lipase having 1,3-position selectivity and the by-product water or lower alcohol formed by the reaction is removed from the system at a reduced pressure to obtain the diglycerides.
Although the esterification or transesterification method is a process in which fatty acids or lower alcohol esters thereof and glycerol are converted to partial diglycerides through a one-step reaction, it is not cost efficient because the individual feedstock materials are expensive.
When a fat is used as the feedstock, steam decomposition of the fat is generally conducted under the conditions of 50 to 60 kg/cm.sup.2 and 250 to 260.degree. C. However, the decomposition products discolor considerably and, thus, distillation is necessary. Performing a distillation treatment, in the case where a vegetable oil or the like is used as the feedstock, results in a decrease in the yield of about 10%. In addition, active ingredients, such as a phytosterol, that are present in the vegetable oil are lost as a distillation residue.
A representative example of the glycerolysis reaction in which a fat is used as the feedstock is given in JP-B 6-65310. This reference discloses an alcohol group exchange reaction between a fat and glycerol that is conducted in the presence of an immobilized lipase having 1,3-position selectivity, to obtain diglycerides. However, this method requires 10 hours or more for completion of the reaction and is unsatisfactory in industrial productivity.